A pressurized light water reactor operation is an established operation which is normally carried out with a high degree of reliability. In such reactors, a reactor vessel is positioned in a refueling pool cavity formed by a wall of the concrete shielding structure in a containment device. The refueling pool cavity has instruments positioned therein for monitoring reactivity. The refueling pool and the refueling pool cavity accomodate thermal expansion of the reactor during operation and provide a path for air flow from the bottom of the reactor vessel. Prior to refueling the reactor, the refueling pool is flooded with berated water to provide neutron shielding while the reactor vessel head is removed. To protect instrumentation in the refueling pool cavity, it is necessary to install a seal plate over the cavity before the water is added.
During normal reactor operations the reactor vessel is subjected to radial and axial thermal expansion. Consequently, the seal plate currently in use for refueling operation can not be left installed around the reactor vessel and the refueling pool floor in the concrete shielding structure after refueling because it is unable to accomodate the thermal expansion of the reactor vessel. Attempts made at developing a permanent pool cavity seal, that does not require removal after refueling, have, as yet, not been completely successful.